1. Field of the Invention
The present invention relates to “hot swapping” controllers and more particularly for hot swapping while drawing about zero current from an onboard charge pump. “Hot swapping” refers to inserting and removing a circuit into or out of a computer system, without removing or powering down the system.
2. Background Information
In the past, power was disconnected while plugging and unplugging circuits into computer or other such electronic systems. This was necessary since the random making and breaking of contacts as a circuit board or module was being inserted or removed from a connector could harm the circuits and/or the system. The possible mis-connections to power, ground and signal inputs and outputs were not controlled.
However, the need to disconnect and later re-connect power is onerous, especially where entire systems may have to be powered down, possibly in set sequences, and later powering up, possibly in set sequences, and re-establishing conditions may take too much time. Moreover, any errors in powering down or up could create high currents and power glitches that may harm the circuits.
Today, it is common to plug and unplug and plug circuits, memories, controllers, etc., into electronic systems without removing power. However, these hot swapping circuits take up valuable space in such systems and often must be located externally with respect to the system they are protecting.
U.S. Pat. No. 6,400,203 to Bezzi et al. ((Bezzi), entitled “Hot Swap Current Limit Circuits and Methods,” is directed to current limiting circuits that may be “hot swapped.” Bezzi, in his FIG. 1, illustrates an example of his invention using a sense resistor, Rsense. This sense resistor is in series with the load current and the voltage across the sense resistor is used to control the load current involved. The use of a series sense resistor limits the voltage dynamic range of the circuit during normal operations, dissipates power and increases the impedance of the circuit.
Another U.S. Pat. No. 6,275,395 to Inn et al. (Inn), entitled “Accelerated Turn-off of MOS Transistors by Bootstrapping,” describes another current limiting circuit. This circuit also uses a sense resistor in series with the load current. It suffers from similar limitations as does the Bezzi patent.
Prior art circuits consume too much die area and power while exhibiting a high “on” impedance (RDSon) of a pass FET and the series sense resistor.